*{
    margin: 0;padding: 0;
}
.header{
    background-color: black;
    color: white;
}
.connent{
    width: 80%;
    margin: 0 auto;
    overflow: hidden;/*清除浮动*/
}
.header_box{
    float: left;
}
.header_box:nth-last-of-type(1){
    width: 25%;
}
.header_box:nth-of-type(2){
    width: 50%;
}
.header_box:nth-of-type(3){
    width: 30%;
    text-align: right;
}
.header_box img{
    height: 50px;
}